IEEE C802.16p-11/0258
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Handling Smart Meter Power Outage – Part: 802.16.1
Date
Submitted
2011-09-10
Source(s)
Bin Chen, George Calcev, Erik Colban,
Ronald Mao
Huawei Technologies
Hung-Yu Wei, Ching-Chun Chou
E-mail: binchen@huawei.com
George.Calcev@huawei.com
ecolban@huawei.com
hywei@cc.ntu.edu.tw
National Taiwan University
Marta Martinez Tarradell, Shantidev
Mohanty
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Intel
Re:
Call for Comments on the new 802.16p Amendment Working Document <IEEE 802.16p11/0022> [based on 802.16.1/D0].
Abstract
This contribution proposes procedures to handle power outages
Purpose
To be discussed and adopted by 802.16p TG
Notice
Release
Patent
Policy
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It
represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for
discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution,
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<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
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IEEE C802.16p-11/0258
Handling Smart Meter Power Outage – 802.16 amendment
Erik Colban, George Calcev, Ronald Mao, Bin Chen
Huawei Technologies
Hung-Yu Wei, Ching-Chun Chou
National Taiwan University
Marta Martinez Tarradell, Shantidev Mohanty
Intel
Introduction
One of the most important features of M2M communication is that it needs to handle a large number of devices
(there may be as many as 12,000 devices in a cell). In some cases the devices are powered by the power grid
and, if a power outage occurs, anywhere between just one or two to several thousand devices may suddenly
loose power. The devices must rely on a charge stored in a capacitor to notify the network about the power
outage, which limits the time (in the order of 150 ~ 250 ms) to carry out the procedure required to notify the
network about the outage. This time limit constrains the set of possible solutions. Also, since the network does
not receive any prior indication about the time and the number of devices affected, the base stations in the
network must be able to handle a power outage at any time without warning and without knowing for how
many devices they need to allocate air interface resources so that the devices can transmit the power outage
notification to the network. When the power outage happens, the devices affected may be in different states,
with some devices in a connected state and other devices in an idle state. The time needed for a device in a
connected state to transmit a message to the network is much shorter than for a device in an idle state, so a
method suitable for devices in a connected state may not be feasible for a device in an idle state. Even for two
devices in a connected state, the procedure for transmitting a message to the base station may vary as a device
that has an allocation on the uplink readily available may use that allocation to transmit a power outage
message, whereas a device that has not been given an allocation on the uplink must first send a bandwidth
request. It is expected that an M2M device will spend most time in an idle state and only enter a connected state
for short durations to transmit low volumes of data (e.g. meter readings). It is very hard to predict how often and
for how long devices will be connected, and this may vary from application to application.
Outline of Proposed Solution
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Figure 1: Power outage procedure
The proposed procedure is illustrated in Figure 1.
a. A power outage occurs affecting any number of M2M devices within the range of a BS. We assume that
the number of devices affected is between 1 and 12000.
b. The M2M device selects a ranging opportunity. The initial backoff window size is chosen by the MS to
be as large as possible such that the M2M device can complete the power outage procedure before it
runs out of power. For example, if the MS has enough power for 360 ms of operation, it shall chose the
initial backoff window to lie within the next 350 ms, keeping 10 ms for the exchange of the two last
messages in this procedure. At the selected ranging opportunity, the M2M device transmits a ranging
code that signals to the BS that the BS must transmit a CDMA Allocation IE in the next frame.
c. Upon detecting the ranging code and identified the special code, the BS shall include a CDMA
Allocation IE in the next UL-MAP providing sufficient bandwidth for the M2M device to send a RNGREQ message that includes a Ranging Purpose Indication.
d. The M2M device sends a RNG-REQ message to the BS. If the MS shares a valid security context with
the target BS so that the MS may include a valid HMAC/CMAC Tuple in the RNG-REQ, then the MS
shall conduct initial ranging with the target BS by sending a RNG-REQ message including the Ranging
Purpose Indication TLV with Bit 5 (Abnormal Power Down Indication) set to 1 and Paging Controller
ID TLVs (11.1.8.2) and a HMAC/CMAC Tuple.
e. If the target BS evaluates the HMAC/CMAC Tuple as valid and can supply a corresponding
authenticating HMAC/CMAC Tuple, then the Target BS may reply with a RNG-RSP message including
the Location Update Response TLV and HMAC/CMAC Tuple completing the abnormal power down
reporting process.
Simulation
We used simulation assumptions described in C802.16p-11/0126 “Evaluation Guideline for Comparison of
Network Entry Solutions”, produced by the 802.16 WG, M2M TG, Network Entry ad-hoc group. In particular
 Number of devices = 12000
 Reporting period = 500 ms (= 100 frames)
 1 ranging opportunity per frame
 Initial backoff window size = 2
 Max backoff window size = 65536
 Max number of retries = 8.
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

T3 timer set to 60 ms
0% misdetection and false alarm probability
We also assumed that if more than one device transmits a code in the same ranging opportunity, the BS will not
detect any code.
For the power outage to be reported, at least one device must select a ranging opportunity that is not selected by
any of the other 11999 devices. Running the simulation 100 times, we observed that this never happened.
Since ranging retries increase the ranging traffic, we tried setting the initial backoff window size to 100 and the
max number of ranging retries to 0 (i.e., each device ranges only once). Yet, we detected no improvement. Note
that the number of devices selecting a given ranging opportunity is Poisson distributed with parameter  = 120.
The probability for a slot to be selected by exactly one device is 120e-120 (which is a ridiculously small number).
We increased the number of ranging opportunities to 16 per frame, and there was still no observable
improvement.
In order to overcome this problem, we simulated an exponential ramp-up function as described in contribution
C802.16p-11/0111. This is equivalent to selecting a ranging opportunity t within the backoff window, not
uniformly, but according to the following cumulative distribution function, where N is a configurable
parameter, and b is the backoff window size:
The remaining assumptions we used were:







Number of devices = 12000, 1200, 120
Reporting period = 500 ms (= 100 frames)
1 ranging opportunity per frame
Initial backoff window size = 100
Max backoff window size = 65536
Max number of retries = 0.
T3 timer set to 60 ms (irrelevant, since there are no retries)
We ran the simulation 10000 times and every time the outage was reported by at least one device. The
distribution of the number of devices that successfully report the outage is shown in Figure 2.
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IEEE C802.16p-11/0258
Figure 2: Distribution of number of devices that successfully report a power outage
[Example of how to read the chart: In almost 1500 out of 10000 simulations in which 1200 devices are affected
by the outage, 11 devices successfully reported the outage.]
Note that when running the simulations for 120, 1200, and 12000 devices, the value of the parameter N was
kept the same. This shows that the method applies with no a priori knowledge of the number of devices that are
affected by the power outage.
Proposed Changes
Change 1: On page 32, modify section 6.3.29 as follows:
>>>>>>>>>>>>>>>>>>>>>>> Change Start <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
6.3.29 Abnormal Power Down Reporting in Connected State
When a MS detects an abnormal power down event, it tries to send an AAI-RNG-REQ message with the
Ranging Purpose Indication indicating that an abnormal or involuntary power down has occurred (value
0b1110).
6.3.29.1 Abnormal Power Down Reporting in Connected State
If the MS is in connected state with uplink bandwidth already allocated and available, then it may use the
available bandwidth to send this AAI-RNG-REQ message containing the Ranging Purpose Indication with
value 0b1110.
If the MS is in connected state but does not have available UL bandwidth, then it may use the procedure defined
in 6.3.6 to request bandwidth. Upon receiving bandwidth allocation it may send the AAI-RNG-REQ message
containing the Ranging Purpose Indication with value 0b1110.
6.3.29.2 Abnormal Power Down Reporting in Idle State
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IEEE C802.16p-11/0258
When an abnormal power down occurs, an M2M device in Idle Mode that has been configured to report
abnormal power down events and that has a valid security association with the Preferred BS shall select a
ranging opportunity within a backoff window starting at the next frame. The M2M device shall set the backoff
window size as large as possible, yet such that it is guaranteed to complete the abnormal power down reporting
procedure before its power is depleted. The M2M shall select the ranging opportunity, t, where t = 1, …, b,
within the backoff window according to the cumulative distribution function
, where
is the backoff window size and N is the value of the configurable system parameter Abnormal Power
Down Ranging Opportunity Selection Parameter (see Table 982). At the selected ranging opportunity the M2M
device shall transmit the Abnormal Power Down Ranging Preamble Code, which is also a configurable system
parameter (see Table 982).
The BS, upon receiving the ranging code, may include a CDMA Allocation A-MAP IE in the next frame
identifying the M2M device and provide an allocation sufficiently large to allow the M2M device to transmit a
AAI-RNG-REQ message including a Ranging Purpose Indication and the CMAC Tuple. Upon receiving this
allocation, the M2M device shall transmit a AAI-RNG-REQ message including a Ranging Purpose Indication
with value 0b1110 (power outage) and a valid CMAC Tuple. The M2M device shall not repeat sending of a
ranging code if it does not receive an allocation from the BS.
If the target BS evaluates the CMAC Tuple as valid and can supply a corresponding authenticating CMAC
Tuple, then the Target BS may reply with an encrypted AAI-RNG-RSP message including the Location Update
Response indicating success completing the abnormal power down reporting process.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Change end <<<<<<<<<<<<<<<<<<<<<<<<<<
Change 2: On page 37, insert the following:
>>>>>>>>>>>>>>>>>>>>>>> Change Start <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
[Modify section Table 982 (Parameters and constants) as indicated:]
System
MS
Name
NMS_max_neighbors
M2M Device
Abnormal Power
Down Ranging
Opportunity Selection
Parameter
M2M Device
Abnormal Power
Down Ranging
Preamble Code
Time Reference
Maximum size of
neighbor list.
Constant used in
defining the CDF
used for selecting a
ranging opportunity to
report an abnormal
power down event in
Idle State. Refer to
section 6.3.29.2.
Ranging preamble
code used to indicate
an abnormal power
down event. Refer to
section 6.3.29.
Minimum Value
32
Default Value
--
Maximum Value
255
--
--
--
--
--
--
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Change end <<<<<<<<<<<<<<<<<<<<<<<<<<
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